I am building a light flyrod Sage XP 3 wt. The wood insert for my nickel silver reel seat was initially just small enough in ID that it would not slide down to the bottom of the blank. I’ve carefully filed the insert until it now fits just about perfectly, with just a very small amount of slack. Do I need to open up the ID sufficient to insert arbors? If so, how much larger should the ID be than the blank?

Alternatively, can I simply rough up the inside of the insert and epoxy without using arbors? What is the best course of action here?

The purpose of these arbors or bushings is to take up any space between the blank and seat. If you do not have any space to take up, then you do not need arbors.

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Arbor are used to take up slack. If you have no room to put a arbor in you can use tape to take any space.
Good luck Bob

Tony: Another purpose for arbors is to transmit touch through the seat(where you put your hand on you reel) example. spinning or casting your hand is on the reel seat. On a flyrod, this is not the case (your hand is on the grip.) so technically there is no need to use arbors. This is an addendeum to the above info. Tom and Bob are right. Just make sure it is centered on the blank. If it was way oversize you may bush it out with 2or 3 bands of masking tape and fill in with epoxy. Just clean the blank good with alcohol to remove any residue that may prevent the epoxy from adhereing. So your answer is : No.